Fuel injection systems

ABSTRACT

A fuel injection system in which fuel flow through the injector nozzles is controlled by electrically operable interrupter valves. Electrical pulses to operate the interrupter valves are generated at constant frequency and the length of the pulses is varied with an engine operating parameter, for example engine air intake. Suitable pulse generating circuits and an arrangement for varying the pulse length with air intake are described.

United States Patent Jackson [54] FUEL INJECTION SYSTEMS [72] Inventor: Harold Ernest Jackson, Devon, En-

211 Appl. No.: 46,201

[30] Foreign Application Priority Data June 27, 1969 Great Britain ..32,531/69 Sept. 17, 1969 Great Britain ..45,806/69 [52] US. Cl. ....l23/32 EA, 123/119 R, 123/139 AW [51] Int. Cl ..F02m 51/00 [58] Field of Search ..l23/l19, 32 EA, 139.17, 32,

[151 3,683,870 [4 1 Aug. 15, 1972 Mennessonm. 123/32 EA Primary Examiner-Laurence M. Goodridge Assistant Examiner-Cort Flint Attorney-Holc0mbe, Wetherill & Brisebois ABSTRACT A fuel injection system in which fuel flow through the injector nozzles is controlled by electrically operable interrupter valves. Electrical pulses to operate the interrupter valves are generated at constant frequency 123,139 and the length of the pulses is varied with an engine operating parameter, for example engine air intake. Suitable pulse generating circuits and an arrangement [56] References cued for varying the pulse length with air intake are UNITED STATES PATENTS descflbed- 3,314,407 4/ 1967 Schneider 123/ 148 E 13 Claims, 12 Drawing Figures FEEDBACK NE TWORK SAWTOOTH TRIGGER POWER GENERATOR CIRCUIT AMPLIFIER 301 302 303 l44R/ABLE RECT/F/ER (ii Eli OCS/LLATOR INDUCTUR NETWORK 83 I I 5%,. 304 305 305 aa flg 303 F300;: 83%

70 AIR VALVE PATENTEDAUG 1 s 1912 SHEET u 0F 6 FEEDBACKT\304 NETWORK SAWTOOTH TR/GGER POWER GENERATOR CIRCUIT 'AMPL/F/ER VAR/ABLE RECTIFIER 83 UCSILLATUR INDUCTOR NETWORK 83 :\300A 03 y l 10 AIR vALvE 4 PATENTEU M15 1 5 I972 3.683; 8 7O sum 5 or 6 VOLTA6E- TIME f X3 v+ x LP, F3 TIME FIG. 6.

ac. BIAS LEVELS TIME:-

FUEL INJECTION SYSTEMS This invention relates to fuel injection systems for internal combustion engines and, in particular,.to systems in which the injection of fuel is intermittent rather than continuous.

In known systems employing intermittent injection, fuel is injected in timed relation to engine operation, the injection being controlled by an engine-driven mechanical or electrical device.

The present invention provides a fuel injection system for an internal combustion engine, including at least one fuel injection nozzle connected to receive fuel from a fuel flow path, at least one fuel interrupter valve actuable to control fuel flow through the injector nozzle(s), and an interrupter valve control mechanism operable to trigger'the interrupter valve(s) into actuation at regular time intervals and responsive to at least one engine operating parameter to adjust the period of time for which the or each interrupter valve is actuated in response to variations in the said engine operating parameter(s).

During operation of the system, fuel supplied to an injector nozzle is discharged intermittently, the period of time over which discharge occurs, and hence the amount of fuel supplied to the engine being dependent on at least one engine operating parameter. The control mechanism may, for example, be operable to open the interrupter valve(s) to permit fuel flow through the injector nozzle(s) and to adjust the period of time for which the or each interrupter valve remains open.

The control mechanism may be operable to generate electrical operating pulses to actuate the interrupter valve(s). The control mechanism may, for example, be operable to generate operating pulses at the said regular time intervals, and to adjust the pulse length in response to variations in the said engine operating parameter(s).

The control mechanism may include an operating pulse generating circuit at least one component of which is responsive to the said one engine operating parameter and adjustable in response to variations in that parameter to adjust the operating pulse length. In an embodiment of the invention, the operating pulse generating circuit is an astable multivibrator circuit including at least one resistive component which is responsive to the said one engine operating parameter and is adjustable in response to variations in that parameter to adjust the operating pulse length.

In another form of the invention, the control mechanism includes a reference voltage generator operable to generate a reference voltage which varies periodically with time, a control signal generator operable to generate a control signal which varies in response to variations in the said one engine operating parameter, and an operating pulse generator responsive to the reference voltage and'the control signal to generate an operating pulse when the reference voltage bears a predetermined relationship to the control signal. In an embodiment of this form of the invention the reference voltage generator is a sawtooth waveform generator and the control signal generator is operable to generate a bias voltage the level of which varies in response to variations in the said one engine operating parameter, the operating pulse generator being operable to generate an operating pulse when the reference voltage exceeds the bias voltage.

The said one engine operating parameter to which the interrupter valve control mechanism is responsive may be engine air intake. The system may, for example, include an engine air intake responsive mechanism operable to produce a control pressure differential in the engine air supply path and adjustable to maintain the control pressure differential ata substantially constant value, the interrupter valve control mechanism being operable to adjust the interrupter valve actuation period in response to adjustment of the air intake responsivemechanism.

The system may also include: a fuel pressurizing device connected in the fuel flow path and operable to pressurize fuel in dependence on at least one engine operating parameter, for example engine air intake.

By way of example, a fuel injection system constructed in accordance with the invention will be described with reference to the accompanying drawings, in which:

FIG. 1 is a diagram of the system;

FIG. 2 is a circuit diagram of a component of the system; a

FIG. 3 is a cross-section through the nozzle;

FIG. 4 is a block circuit diagramof an alternative form of the component illustrated in FIG. 2, and

FIGS. 5 to 8 illustrate the variation of voltage with time at various points in the circuit of FIG. 4.

In the system shown in FIG. 1, fuel is drawn from a tank 1 and supplied by any suitable form of pump 2, for example an electric, gear pump, to a supply conduit 52. Fuel passes from the conduit 52. to a further supply conduit 63 at a pressure determined by a control valve mechanism 100, and excess fuel is returned to the tank 1 via a chamber 53 in mechanism 100, a conduit 56, a relief valve 57 and a conduit 61. The conduit 63 leads to thefuel injector nozzles 83 via a check valve 63A and excess fuel is returned from the nozzles to the tank 1 via a restrictor 61A and the conduit 61.

The injectors 83 are air-bled solenoid-operated nozzles and will be described below. Operation of the nozzles to discharge fuel is controlled by a unit 200 in dependence on a suitable engine operating parameter: in the system illustrated, the parameter is engine air intake as will be described below. The pressure control mechanism also operates in dependence on engine air intake and the operation of this mechanism will also be described below.

The system also includes a fuel/air mixture enrichment valve 101A which, although an advantageous feature, is not essential to the operation of the system.

' The function of the injector control unit 200 will now be described. The unit is designed. to produce a pulsating DC. voltage when connected to a suitable source of electrical power 201, the pulses occurring at a suitable constant frequency. The pulses are applied to the operating solenoids of the injectors 83 which are connected, as shown, to the output terminals of the unit 200. The injectors 83 are thus caused to open at regular intervals (determined by the commencement of each one of the pulses from unit 200) to discharge fuel supplied through the conduit 63. The fuel is discharged into the mixture induction manifold of the engine, to be drawn into the engine cylinders, and when the operating pulse from unit 200 terminates, the injectors close and fuel discharge ceases. As will be described below, the length of the pulses generated by unit 200 and hence the period for which the injectors remain open is dependent on engine air intake.

A circuit diagram of the unit 200 is shown in FIG. 2. The unit is, as can be seen from FIG. 2, a combination of a conventional astable multivibrator stage 210 and a complementary power output stage 211 and, when the power source 201 is connected across the input terminals 202 a pulsating DC. voltage is produced at the output terminals 203. The circuit shown in FIG. 2, being formed of conventional components, will not be described further, but it will be noted that the length (but not the frequency) of the output pulses can be adjusted, in known manner, by varying the position of the slider 204 of the potentiometer 205 in the multivibrator stage 210. A suitable output pulse frequency is 50 cycles/sec. Preferably, the control unit 200 (without the potentiometer 205) is formed as a unit which is easily removable from the system and replaceable in case of failure. It is not essential for the pulse-generating circuit of unit 200 to take the form shown in FIG. 2 and any other suitable pulse-generating circuit could be used. Other forms of control unit are also possible and one suitable alternative form will be described below with reference to FIGS. 4 to 8.

In FIG. 1 the potentiometer 205 comprising slider 204 and resistor 206 is shown located outside the unit 200 to demonstrate the adjustment of the unit in dependence on engine air intake. The position of slider 204 is controlled by a cam 207 which co-operates with a follower 208 on which the slider 204 is mounted. The

cam 207 is coupled to the control lever 7 of an air valve 4 located in the conduit 3 which feeds air to the engine in the direction left to right as seen in the drawings. The function of the air valve 4 will be described below. Also located in conduit 3 is the customary throttle valve 1.

The lever 7 is also coupled to one side of a piston 8A located in a cylinder 8B. On the other side of the piston, the cylinder 88 is connected, by a conduit 18 including a restrictor 18A, to a chamber 20 in a manifold depression control unit 102. The unit 102 functions through the air valve 4 to maintain a constant depression in the air intake conduit 3 between the air valve 4 and the throttle valve 1. The manner of operation of the unit 102 is exactly the same as that of the mechanism 102 described in my copending U.S. Pat. application Ser. No. 31,316 filed Apr., 23, 1970.

The chamber 20 of manifold depression control unit 102 can communicate with a further chamber 90 in the unit under the control of a ball valve 21A co-acting with a seat 22. A control rod 91 extending from the chamber 90 through an O-ring seal 92 and into a chamber 93 couples the ball valve 21A to a diaphragm 24 which separates the chamber 93 from a further chamber 94 open, in the absence of conduit 130, to atmosphere). The rod 91 is capable of rocking movement in the seal 92 and a spring 27 located in chamber 94 acts on the diaphragm 24 and hence on rod 91 to urge the ball valve 21A away from the seat 22. A conduit 29 joins chamber 93 to the air intake conduit 3 between the valves 1 and 4, and a conduit 95 including a restrictor 95A connects the chamber 20 to the chamber 53 of the pressure control valve mechanism 100.

It was mentioned above that chamber 53 receives excess fuel from the supply conduit 52 and is connected, via relief valve 57 to the fuel tank 1. The chamber 53 is,

in fact, connected to a chamber 64 of the relief valve 57, and the chamber 64 can communicate, under the control of a diaphragm 58, with the conduit 61 leading back to the fuel tank 1. The diaphragm 58 is loaded, by a spring 59, against a valve seat 60 separating chamber 64 from conduit 61, and thereby maintains a substantially constant fuel pressure in chamber 64 and hence in chamber 53.

In operation of the system, the air valve 4 is urged towards a closed position by a spring 30. When the throttle valve 1 is opened (the air valve 4 being in the closed position) there is created a depression in the conduit 29 which draws down the diaphragm 24, so closing the ball valve 21A. The substantially constant pressure determined by the relief valve 57 is then applied fully, via conduit 18, on the piston 8A causing the latter to move upward (as seen in FIG. 1) and, through lever 7 to open the air valve 4. Any leakage of fuel across the piston 8A is returned to the tank 1 through a conduit 97. The opening of air valve 4 reduces the depression in conduit 29 and, through diaphragm 24 opens the ball valve 21A allowing fuel to leak from chamber 20 into chamber and to be returned to the tank 1 via conduit 96 The fuel pressure acting on piston 8A is thereby reduced and the piston moves downwards (as seen in FIG. 1) to close the air valve 4. In this manner, the position of the air valve 4 adjusts to maintain a substantially constant depression in that portion of the conduit 3 between the valves 4 and l, the depression being determined by the setting of the control mechanism 102 and, in particular, by the strength of the spring 27. It is to be noted that, provided the pressure in chamber 93 required to drive the ball valve 21A fully open is less than the substantially constant relief valve pressure, the strength of spring 30 and the effects of friction in the piston 8A, the linkage 6, 7 etc. are in no way effective in altering the constant depression in the conduit 3 by any substantial amount. The valve of the restrictor 95a is chosen to give a desired opening speed to the ball valve 21A.

The air valve 4, as mentioned above, coupled to the potentiometer 205 of the control unit 200 so that, as the air valve 4 opens, the length of the operating pulses applied to the injectors 83 increases and more fuel is fed to the engine.

The construction of the manifold depression control unit 102 is such that the O-ring seal 92 serves the purpose of sealing chamber 93 (which is exposed to the depression produced in the air intake conduit 3 between the valves 1 and 4) from the chamber 90 (which contains fuel). The seal 92 is partly located in a groove in the rod 91 and partly in a groove in the housing of the unit and this particular construction permits rocking movement of the rod 91 as described above but prevents axial movement and minimizes friction and wear. In particular, the need for sliding or rotating seals between depression zones and pressurized fuel zones is overcome.

An injector nozzle 83 is shown in greater detail in FIG. 3. The nozzle has a fuel inlet which, in use, is connected to the fuel supply conduit 63. The inlet 140 communicates, via a passage 141 with the interior of a tubular interrupter valve member 142, which, in turn, communicates through ports 143 in the valve member wall with a chamber 144. A spring 145 seated on an end portion of the valve member 142 biases the valve member against a seating 146, in which position communication between the chamber 144 and a fuel tube 147 is cut-off by the valve member. The fuel tube 147 is a small diameter stainless steel tube and is aligned with an outlet orifice 148 in an outer jacket 149 surrounding the tube. The space between the tube 147 and the jacket 149 is vented through ports 150. Movement of the valve member 142 is controlled by a solenoid 151 within which the valve member is partly located. The valve member 142, or at least that portion of the valve member which is located within the solenoid is formed of a magnetizable material so that energization of the solenoid 151 moves the valve member away from the seating 146 and allows fuel to flow into the fuel tube 147. Fuel is discharged through the outlet orifice 148 into the mixture induction manifold of the engine, air being drawn into the jacket 149 through the ports 150. In use of the injector in the system shown in FIG. 1, the solenoid 151 is connected to the output terminals of the control unit 200, the valve member 142 thereby being moved to an open position at regular time intervals and held in that position for a length of time determined by the length of the output pulses from unit 200.

The use of air-bled nozzles as shown in FIG. 3 is advantageous in that the effect on fuel flow of the depression in the manifold in which the nozzles are located is thereby eliminated. If air-bled nozzles are not employed, the effect may be eliminated by subjecting the upper surface (as seen in the drawing) of the diaphragm of relief valve 57 to the manifold depression. The nozzle shown in FIG. 3 has the further ad vantage that the fuel tube 147 acts as a fuel restrictor and, when a plurality of nozzles are connected in a system, serves to equalize fuel distribution between the nozzles. It will be appreciated that the use of the nozzle shown in FIG. 3 is not restricted to the system shown in FIG. 1.

It was mentioned above that valve mechanism 100 controls the pressure at which fuel is supplied to injectors 83. The mechanism 100 is exactly the same as the pressure control mechanism 100 described in my copending US. Pat. application Ser. No. 31,316 filed Apr. 23, 1970 and functions to increase the pressure of fuel supplied to the injectors 83 as the air flow through conduit 3 increases. To this end, the conduit 3 includes a closed end slot 41 which communicates with a conduit 43 leading, via a restrictor 44, to a chamber 45 in the control mechanism 100. A diaphragm 47, bounding the chamber 45, is coupled to one end of a control rod 110 (similar to rod 91 in the manifold depression control unit 102) which extends through a seal 111 into the chamber 53 and carries, at its other end, a pressure control valve member 112. The valve member 112 cooperates with a seating 113 to control fuel flow from the supply conduit 52 into the chamber 53. The rod 110 is capable of rocking movement in the seal 111 and movement of the valve member 112 is controlled, through the rod, by the diaphragm 47. The chamber 53 is connected, by conduit 56 to the relief valve 57, as described above, the chamber 53 thereby being pressurized to the substantially constant relief valve pressure.

When the engine is not running, atmospheric pressure exists throughout the air intake conduit 3, and

side of the diaphragm 47 to chamber 45 is also, in the absence of conduit 130, exposed to atmospheric pressure so that there is no pressure differential across the diaphragm. The pressure in supply conduits 52 and 63 is then the same as that in chamber 53. When the engine is running with its air consumption at a minimum (which is the idling mode of operation) the position of the air valve 4 is such that the right hand end of slot 4] lies just on the right side of air valve 4 (this position being shown in FIG. 3). As a result, a small proportion of the constant depression developed in conduit 3 between the valves 1 and 4 is applied to conduit 43.

The enrichment valve 101A (which will be described below) is normally open and, for the present, it is sufficient to state that, under these circumstances and in the absence of conduit 130, atmospheric air can pass via restrictors 66A and 668 in the valve 101A into the conduit 43 so weakening the depression signal applied to diaphragm 47. The weakened depression signal applied to diaphragm 47 acting through rod 1 l0 urges the valve member 112 towards the seat 113 and, as a result, the fuel pressure in supply conduits 52 and 63 rises until equilibrium is restored. As the air consumption of the engine increases, air valve 4 opens further and, in doing so, exposes a greater length of the slot 41 to the constant depression between valves 4 and l. The increased depression (again weakened by atmospheric air admitted through restrictors 66A and 663 in valve 101A) is applied to diaphragm 47 and results in an increased closing force on valve member 112 causing a further rise in fuel pressure in supply conduits 52 and 63. During acceleration, if the throttle valve 1 is suddenly opened the depression between the valves 4 and l rises suddenly. The increase is effective immediately, through diaphragm 47 and valve member 112 to raise the fuel pressure in supply conduits 52 and 63.

It will be appreciated however that the use of the pressure control mechanism shown in FIG. 1 is not essential to the system and that. other forms of fuel pressurizing device could be employed.

The relief valve 57 which, as mentioned above, maintains a substantially constant pressure in chamber 53 and a predetermined minimum pressure value in supply conduits 52 and 63 is preferably so adjusted that the minimum pressure value is sufficient to ensure that fuel in the system remains liquid at all times, even when fuel temperature rises considerably above normal ambient temperature.

The check valve 63A located in the fuel supply line to injector devices 83 functions "to enrich the fuel/air mixture supplied to the injectors under engine acceleration conditions, as may be seen from the following example:

Suppose that the normal depression between valves 1 and 4 in conduit 3 is 1 inch Hg; that the resultant fuel pressure in supply conduit 63 is 10 p.s.i.; that the substantially constant minimum pressure imposed by relief valve 57 is 15 p.s.i. and that the check valve 63A is biased by a spring 76 which imposes a substantially constant load equivalent to 17 p.s.i. Under steady conditions the fuel metering pressure is then 10 15 I7 8 p.s.i.

0n sudden acceleration, before the position of the air valve 4 has been adjusted, the depression between valves 1 and 4 may rise momentarily, for example to 2 inch Hg. This in turn raises the fuel pressure in conduit 63 to 20 psi. The metering pressure is now 20 15 17 18 psi. Thus, while the depression has changed in the ratio 2/1 the fuel metering pressure has changed in the ratio 2.25/1, providing enrichment during acceleraq tion. When the air valve 4 has opened to restore the 1 inch Hg depression between valves 1 and 4, the fuel metering pressure reverts to its original value but the new position of the air valve 4 is accompanied by readjustment of the potentiometer 205.

The check valve 83A also performs the secondary, but important, function of preventing fuel-from being delivered to the injectors when the engine is not turnmg.

It will be seen from the above description that, in operation of the system fuel is supplied to the injector devices 83 at a pressure that is dependent on engine air intake and that the injectors open at regular time intervals but remain open for a length of time that is also dependent on engine air intake. It will be appreciated, however, that it is not essential for fuel pressure to be controlled by engine air intake and that another engine operating parameter could be employed. Alternatively, several operating parameters of which one may be air intake could be employed. Furthermore, the use of engine air intake to determine the length of time for which the injector nozzles remain open is also not essential and another engine operating parameter could be employed. Alternatively, several operating parameters of which one may be air intake could be employed. When control is effected by engine air intake it will be appreciated that it is not essential for arrangements utilizing the maintenance of a constant depression in the engine air intake to be employed.

It will also be appreciated that the arrangement shown in FIG. 1 for maintaining a constant depression in air intake conduit 3 and for thereby controlling pulse unit 200 and pressure control valve mechanism 100 could be replaced by the mechanism described in my copending U.S. Pat. application, No. 31,315, filed Apr. 23, 1970.

The valve 101A which has been mentioned above is a manually operated valve which functions to enrich the fuel/air mixture supplied to the engine, for example when the engine is cold. The operation of the valve 101A will now be described.

When valve 101A is open, atmospheric air is admitted, as described above, to conduit 43 via restrictors 66A and'66B in the valve. The restrictor 66A can be closed manually to restrict the flow of atmospheric air into conduit 43 and thereby increase the effective depression applied to diaphragm 47 and raise fuel pressure in the supply conduits 52 and 63. The result is that the engine receives a richer fuel/air mixture. The restrictor 668 which remains open under all operating conditions is adjustable to vary the setting of valve 101A.

It will be appreciated that, although valve 101A was referred to above as having utility under engine starting conditions it is not restricted to use under these conditions and could, being a manually-operated valve, be used whenever a richer fuel/air mixture is required. It will also be appreciated that the valve 101A is not essential to the functioning of the manifold depression control unit 102 or (except in so far as it provides a restriction 66A, 668 through which atmospheric air is admitted to conduit 43) to the functioning of the pressure control mechanism the valve 101A could, accordingly, be omitted.

The conduit which is shown in dotted lines in FIG. 1 and which, in the above description, was assumed to be absent, connects the air intake conduit 3 on the atmospheric side of the valves 1 and 4 to the chamber 94 in the manifold depression control unit 102 and also to the chamber 131 in the pressure control mechanism 100 and the atmospheric air inlet of the enrichment valve 101A. The purpose of this conduit 130 is to nullify any effect on the depression between valves 1 and 4 of the flow resistance of the air cleaner normally included in the inlet of air intake conduit 3. This flow resistance could have a particularly noticeable effect under high engine power conditions: the conduit 130 is, however, not essential and, as described above, chambers 131 and 94 and the inlet of valve 101A could be left open to atmosphere.

The alternative form of control unit mentioned above and shown in FIG. 4 to 8 would, in use, replace the control unit 200 including the potentiometer 205 in FIGS. 1 and 2. The components of the alternative control unit are illustrated diagrammatically in FIG. 4 and include a sawtooth waveform generator 301 the output of which is connected to the input of a trigger circuit 302. The trigger circuit 302 produces the operating pulses for the injector devices 83, the output of the trigger circuit 302 being connected to the operating solenoids of the injector devices 83 through a power amplifier 303. The output of the trigger circuit 302 is also connected back to the input of the sawtooth waveform generator 301 through a feed back network 304.

The sawtooth waveform generator 301 produces a constant frequency output voltage as illustrated in FIG. 5: a suitable frequency is 50 cycles/sec. The trigger circuit 302 produces a square output pulse when the input from the generator 301 exceeds a predetermined value determined by a control circuit 303. This predetermined value is variable in dependence on engine air intake, as will be described below, to adjust the length of the trigger circuit output pulse. The output frequency of the trigger circuit 302 is, however, constant and corresponds to the output frequency of generator 301.

The control circuit 303 also includes an oscillator 304, a variable inductor 305 and a rectifier network 306. The oscillator 304 produces an output of fixed frequency, for example 1,000 cycles/sec. which is fed to the variable inductor 305. The inductor 305 is coupled, in any suitable manner, (as indicated at 300A in FIG. 4) to the air valve 4 in the engine air intake conduit 3 (FIG. 1) whereby movement of the air valve 4 to maintain a constant depression in the intake conduit 3 as described above will adjust the inductor 305. The inductor 305 may, for example, be coupled to the air valve lever 7 through a cam and cam follower in the manner described above and illustrated in FIG. 1 for the potentiometer 205. Adjustment of the inductor 305 changes the amplitude of the output of oscillator 304 and the modified output is fed to the rectifier network 306. In this network the signal is rectified and smoothed to produce a dc. bias signal which is applied (that is, for three values of engine air intake). FIG. 7 I

shows the output of the rectifier network 306 for the same three values of inductance.

FIG. 8 illustrates the manner in which the d.c. bias signal from the control circuit 303 controls operation of the trigger circuit 302. In FIG. 8dthe d.c. bias signals for inductance values X X and X are shown superimposed on the output of generator 301. The trigger circuit 302 produces an output pulse when the output of generator 301 exceeds the bias signal from control circuit 303: FIGS. 8a, 8b and 80 show the output of trigger circuit 302 for inductance values X X and X respectively from which it can be seen that the output frequency of the trigger circuit remains constant but that the length of the trigger circuit output pulses decreases as the d.c. bias level applied by control circuit 303 increases. The length of the trigger circuit output pulses determines the length of time for which the injector nozzles 83 are open. The length of time for which the injector nozzles 83 are open is thus dependent on engine air intake, as with the control unit shown in FIG. 2.

The components illustrated diagrammatically in FIG. 4, that is, generator 301, trigger circuit 302 etc. are well known and need not, therefore, be described in detail. It will be appreciated, however, that the sawtooth generator 301 could be replaced by a generator of any other suitable reference voltage waveform. In addition, other arrangements could be employed (instead of the oscillator 304 and variable inductor 30S illustrated) to generate an oscillating control signal the amplitude of which is dependent on engine air intake.

Preferably this alternative form of control unit is also a unit which is easily removed from the fuel injection system and can be replaced in case of failure.

Finally, it should be appreciated that although the systems described above employ a plurality of injector devices 83 each incorporating a solenoid-operated interrupter valve, that is not essential and the plurality of solenoid-operated injector devices could, for example, be replaced by a single solenoid-operated interrupter valve operable intermittently by the control unit 200 (FIG. l) to feed fuel to a plurality of open injector nozzles via respective pressure-responsive control valves. An arrangement of this type is disclosed in my copending US. Pat. application Ser. No. 91,937 filed Nov. 23, 1970.

lclaim:

1. A fuel injection system for an internal combustion engine, including a source of fuel under pressure, a fuel flow path, at least one fuel injector nozzle connected to receive fuel from the fuel flow path, at least one electrically operable fuel interrupter valve actuable to control fuel flow through the injector nozzle(s), and an electrical control circuit arrangement operable to generate electrical operating pulses at a continuous constant frequency independent of engine operation and connected to apply said pulses to the interrupter valve(s) to actuate the interrupter valves(s), said control circuit arrangement including means electrically connected in said circuit arrangement and responsive to at least one engine operating parameter to adjust the length of said operating pulses, and thereby adjust the period of time for which the or each interrupter valve is actuated, in response to variations in the said engine operating parameter(s).

2. A system as claimed in claim 1, in which the control circuit arrangement is operable to generate the operating pulses to open the interrupter valve(s) to permit fuel flow through the injector noule(s).

3. A system as claimed in claim 1, in which the control circuit arrangement is an astable multivibrator circuit including at least one resistive component which is responsive to the said one engine operating parameter and is adjustable in response to variations in that parameter to adjust the operating pulse length.

4. A system as claimed in claim 1, in which the control circuit arrangement includes a reference voltage generator operable to generate a reference voltage which varies periodically with time, a control signal generator operable to generate a control signal which varies in response to variations in the said one engine operating parameter, and an operating pulse generator responsive to the reference voltage and the control signal to generate an operating pulse when the reference voltage bears a predetermined relationship to the control signal.

5. A system as claimed in claim 4, in which the reference voltage generator is a sawtooth waveform generator and the control signal generator is operable to generate a bias voltage the level of which varies in response to variations in the said one engine operating parameter, the operating pulse generator being operable to generate an operating pulse when the reference voltage exceeds the bias voltage.

6. A system as claimed in claim 4, in which the control signal generator includes means operable to generate an oscillating voltage the amplitude of which varies in response to variations in the said one engine operating parameter.

7. A system as claimed in claim 6, in which the oscillating voltage generator includes an inductive component which is responsive to the said one engine operating parameter and is adjustable in response to variations in that parameter to vary the amplitude of the oscillating voltage.

8. A system as claimed in claim 1, in which the said one engine operating parameter is engine air intake.

9. A system as claimed in claim 8, including an engine air intake responsive mechanism operable to produce a control pressure differential in the engine air supply path and adjustable to maintain the control pressure differential at a substantially constant value, the control circuit arrangement being operable to ad just the interrupter valve actuation period in response to adjustment of the air intake responsive mechanism.

10. A system as claimed in claim 1, including a fuel pressurizing device connected in the fuel flow path and operable to pressurize fuel in dependence on at least one engine operating parameter.

11. A system as claimed in claim 10, in which the said one engine operating parameter is engine air intake.

response to adjustment of the air intake responsive mechanism.-

13. A system as claimed in claim 1, including a plurality of interrupter valves each actuable to control fuel flow through a respective injector nozzle. 

1. A fuel injection system for an internal combustion engine, including a source of fuel under pressure, a fuel flow path, at least one fuel injector nozzle connected to receive fuel from the fuel flow path, at least one electrically operable fuel interrupter valve actuable to control fuel flow through the injector nozzle(s), and an electrical control circuit arrangement operable to generate electricAl operating pulses at a continuous constant frequency independent of engine operation and connected to apply said pulses to the interrupter valve(s) to actuate the interrupter valves(s), said control circuit arrangement including means electrically connected in said circuit arrangement and responsive to at least one engine operating parameter to adjust the length of said operating pulses, and thereby adjust the period of time for which the or each interrupter valve is actuated, in response to variations in the said engine operating parameter(s).
 2. A system as claimed in claim 1, in which the control circuit arrangement is operable to generate the operating pulses to open the interrupter valve(s) to permit fuel flow through the injector nozzle(s).
 3. A system as claimed in claim 1, in which the control circuit arrangement is an astable multivibrator circuit including at least one resistive component which is responsive to the said one engine operating parameter and is adjustable in response to variations in that parameter to adjust the operating pulse length.
 4. A system as claimed in claim 1, in which the control circuit arrangement includes a reference voltage generator operable to generate a reference voltage which varies periodically with time, a control signal generator operable to generate a control signal which varies in response to variations in the said one engine operating parameter, and an operating pulse generator responsive to the reference voltage and the control signal to generate an operating pulse when the reference voltage bears a predetermined relationship to the control signal.
 5. A system as claimed in claim 4, in which the reference voltage generator is a sawtooth waveform generator and the control signal generator is operable to generate a bias voltage the level of which varies in response to variations in the said one engine operating parameter, the operating pulse generator being operable to generate an operating pulse when the reference voltage exceeds the bias voltage.
 6. A system as claimed in claim 4, in which the control signal generator includes means operable to generate an oscillating voltage the amplitude of which varies in response to variations in the said one engine operating parameter.
 7. A system as claimed in claim 6, in which the oscillating voltage generator includes an inductive component which is responsive to the said one engine operating parameter and is adjustable in response to variations in that parameter to vary the amplitude of the oscillating voltage.
 8. A system as claimed in claim 1, in which the said one engine operating parameter is engine air intake.
 9. A system as claimed in claim 8, including an engine air intake responsive mechanism operable to produce a control pressure differential in the engine air supply path and adjustable to maintain the control pressure differential at a substantially constant value, the control circuit arrangement being operable to adjust the interrupter valve actuation period in response to adjustment of the air intake responsive mechanism.
 10. A system as claimed in claim 1, including a fuel pressurizing device connected in the fuel flow path and operable to pressurize fuel in dependence on at least one engine operating parameter.
 11. A system as claimed in claim 10, in which the said one engine operating parameter is engine air intake.
 12. A system as claimed in claim 11, including an engine air intake responsive mechanism operable to produce a control pressure differential in the engine air supply path and adjustable to maintain the control pressure differential at a substantially constant value, the fuel pressurizing device being operable to vary the pressure at which fuel flows to the injector nozzle(s) in response to adjustment of the air intake responsive mechanism.
 13. A system as claimed in claim 1, including a plurality of interrupter valves each actuable to control fuel flow through a respective injector nozzle. 